A user has had to rebuild his computer. How does he gain access to his license again?

I tried to remove him as a user, so that I could reassign the license to him again.  I have selected the 'All Users' tab, clicked the 'x' against his name, but the narrative 'Manage this license' came up, not the option to 'Remove User'.  Clearly I don't want to remove the license.  What next?